Flagella-Mediated Differences in Deposition Dynamics for Azotobacter vinelandii in Porous Media

Abstract

A multiscale approach was designed to study the effects of flagella on deposition dynamics of Azotobacter vinelandii in porous media, independent of motility. In a radial stagnation point flow cell (RSPF), the deposition rate of a flagellated strain with limited motility, DJ77, was higher than that of a nonflagellated (Fla(-)) strain on quartz. In contrast, Fla(-) strain deposition exceeded that of DJ77 in two-dimensional silicon microfluidic models (micromodels) and in columns packed with glass beads. Both micromodel and column experiments showed decreasing deposition over time, suggesting that approaching cells were blocked from deposition by previously deposited cells. Modeling results showed that blocking became effective for DJ77 strain at lower ionic strengths (1 mM and 10 mM), while for the Fla(-) strain, blocking was similar at all ionic strengths. In late stages of micromodel experiments, ripening effects were also observed, and these appeared earlier for the Fla(-) strain. In RSPF and column experiments, deposition of the flagellated strain was influenced by ionic strength, while ionic strength dependence was not observed for the Fla(-) strain. The observations in all three setups suggested flagella affect deposition dynamics and, in particular, result in greater sensitivity to ionic strength.

MS2 Bacteriophage Reduction and Microbial Communities in Biosand Filters

“…7,8,10,11,28 Build-up of biofilm around sand particles causes a slower flow rate due to more constricted pore spaces as shown in previous studies conducted with two-dimensional microscopic models of porous media. 29,30 A slower flow rate allows for more contact time between the water and sand particles, and hence overall higher reduction. In addition, once the biofilm is developed on the sand surface, the chemical and physical interaction of MS2 virus with the biofilm should also influence MS2 reduction.…”

Swimming Motility ReducesAzotobacter vinelandiiDeposition to Silica Surfaces

“…First, 100 mM KCl was found to be optimal for flagellar motion (de Kerchove and Elimelech, 2007). Second, enhanced column deposition was observed for A. vinelandii cells under 100 mM KCl in our previous work (Lu et al, 2013). A video composed of 1000 images with duration of 31 s was recorded for each strain using an inverted Axio Observer microscope (Carl Zeiss, Oberkochen) and a camera (Andor Technology iXon 897) controlled by Solis software (Andor Technology).…”

“…Three A. vinelandii strains were used: DJ (wild‐type, flagellated, and motile), DJ77 ( nifH − , flagellated but with impaired motility [Jacobson et al, 1989; Lu et al, 2013]), and JZ52 ( nifH − flhC − , nonflagellated and nonmotile [Lu et al, 2013]). Azotobacter vinelandii strains were grown on modified (no molybdenum) Burk's medium plates (Strandberg and Wilson, 1968) with the addition of 0.013 M ammonium acetate at 30°C for 2 d before inoculation into liquid media of modified (no molybdenum, no iron) Burk's medium with addition of 0.013 M ammonium acetate shaking at 170 rpm and 30°C for 18 to 20 h. This growth procedure was designed to induce competence for natural transformation assays and followed here to allow comparisons between transport and natural transformation behavior in A. vinelandii (Lu et al, 2013). The cells were then centrifuged at 1000 g for 10 min, decanted to remove the culture media, and resuspended in the same volume of 3‐morpholinopropane‐1‐sulfonic acid (MOPS) buffer solution with 100 mM KCl at pH 7.2.…”

“…Silicon micromodels of porous media were used to visualize and quantify bacterial deposition in two dimensions under flow conditions. Fabrication, inoculation, and operation of the micromodels were described previously (Lu et al, 2013). A regular pattern of 1440 cylindrical collectors (180 μm diameter, 114 μm in pore‐body size, 28 μm in pore‐throat size, porosity 0.4) was etched to 22 μm depth in a Si wafer as depicted in Fig.…”

“…Different responses to ionic strength and divalent cation concentration have been observed for motile and nonmotile Pseudomonas strains, suggesting differences in the mechanisms controlling their attachments to silica and alginate‐coated surfaces (de Kerchove and Elimelech, 2008a, 2008b). The presence of flagella resulted in greater sensitivity to ionic strength for Azotobacter vinelandii deposition (Lu et al, 2013). At a low fluid velocity (0.56 m/d), swimming Pseudomonas cells were able to avoid attachment in packed‐bed columns (Camesano and Logan, 1998).…”